Patsy McGrath, 76, said she bought the kit from a shop several years ago to help her end her own life, should she need it, after watching her sister die of multiple sclerosis.

Two police officers came to her Nelson home late last week, she said.

"I came home from town and was met by two police walking up the stairs and they had a search warrant. Very clear, these two rather embarrassed policemen had a search warrant for my house, should they need to look over it because I was holding a helium balloon kit.

"They had heard, nobody would tell me why or where or anything, so I gave them the helium because they had the power to take it anyway and I didn't want my house broken to pieces. All I was doing was owning a helium balloon kit."

Mrs McGrath, who donates to pro-euthanasia group Exit International and is a local member of the Voluntary Euthanasia Society, said officers had told her they were there as part of a wider investigation, but it was unclear how they knew she had the kit.

"I was at a meeting in Wellington a couple of weeks ago in which I may have said I did [have the kit]. It was a meeting of like-minded people, but whether there was a bug there or a mole there I've no idea."

Mrs McGrath said, according to the search warrant, the kit would be used for evidence against someone suspected of aiding and abetting suicide, and the search was part of a wider investigation called Operation Painter involving serveral other properties.

Mrs McGrath said she did not plan to seek legal advice because she had not broken any law and police had not taken the matter further.

Police confirmed they had also arrested and charged a Lower Hutt woman with importing a class-C drug as part of an ongoing investigation.

'Political activity'

Voluntary Euthanasia Society president Maryan Street said police had to be careful about how they investigated supporters of the cause.

Ms Street is the author of a petition being heard by Parliament's Health Select Committee seeking medically assisted dying to be legal for terminal illness and unbearable suffering.

She said the police raids on campaigners for voluntary euthanasia smacked of interference into the inquiry.

"There is a political activity going on at the moment and people need to be very circumspect about how they conduct themselves because if they are crashing across a political process then they need to be very clear that there will be a political response."

ACT Party leader David Seymour said the raids raised serious questions about police treatment of a politically sensitive issue.

A spokesperson for Police Minister Judith Collins said she did not even know about the raids until media raised it with her this morning.

She said the minister and her office have not received any information on the matter, and it was an operational matter for police.